The present invention relates to prosthetic systems for the replacement of limbs or portions thereof. More particularly, the invention concerns a modular shoulder prosthesis system that can be used in the extremities that have experienced bone loss or significant, irreparable bone trauma.
For treatment of various problems with the shoulder such as degenerative arthritis and trauma of the shoulder, one method of providing relief to a patient is to replace the articulating surfaces of the shoulder, i.e. the humerus and glenoid articulating surfaces. In such replacement, pin relief, increased motion and anatomic reconstruction of the shoulder joint are goals of the orthopaedic surgeon. With multiple variations in human anatomy, prosthetic systems need to accurately replicated human anatomy with minimal component inventory.
Artificial or prosthetic joints for the extremities are well-known. Many of prosthetic joints are modular, meaning that they include a selection of different components to account for differences in patient anatomy or surgical procedures. For example, U.S. Patent No. 5,314,479, owned by the assignee of the present invention, discloses a modular shoulder prosthesis that includes an array of selectable stems, bodies, collars and head members. The modular prosthesis of the ""479 Patent allows the orthopaedic surgeon to assemble a custom prosthetic joint by selecting different sizes, shapes and orientations of the individual joint components.
As indicated above, current modular prostheses consist of a series of humeral stems and heads for replacement of articulating surfaces. The stems are offered with various metaphysis and diaphysis sizes. Humeral heads are offered in various radiuses of curvature, diameters, and heights. Any locking member used to rigidly attach the humeral head to the humeral stem has a fixed position, offering no means for positional adjustment of version, varus/valgus angulation.
Eccentricity can be addressed using humeral heads with the attachment feature placed off center from the articulating exterior spherical surface. However, the eccentric position of the humeral head is only adjustable about the fixed central axis of the locking member located on the humeral stem. More importantly, version, varus/valgus angulation adjustments are not possible with these embodiments.
In view of the above-noted shortcomings, modular shoulder prostheses have been developed that allow orienting the humeral head in multiple angular positions. Each of these embodiments, however, is deficient in design, and thus each is considered a sub-optimal solution. In U.S. Pat. No. 6,197,062 issued to Fenlin provides a modular shoulder prosthesis that utilizes an offset male taper member. The offset male taper member is rotated about the connecting axis of the humeral stem thus changing the angular position of the humeral head. Some of the problems associated with this particular embodiment include having to completely remove the humeral head to make positional adjustments, and version and varus/valgus angulation adjustments are not independent of one another.
In EP 0712617, a modular shoulder prosthesis is provided that allows positional adjustments of the humeral head. This prosthesis utilizes a split spherical ball and locking set screw to rigidly secure the humeral head in the selected position. While independent adjustment of humeral head position is possible with this prosthesis, such adjustments to humeral head position can only be made when the humeral stem is removed from the humeral canal because of the location of the locking set screw.
In U.S. Pat. No. 5,741,335 and EP 0715836, a shoulder prosthesis is provided that has a locking member consisting of a split spherical ball and locking set screws. A humeral head with a spherical cavity receives the spherical ball. The locking set screws located on the lateral aspect of the humeral stem below the head resection plane advances a pusher that compresses the ball against the humeral head stem while locking the ball against the cavity to lock the humeral head in place. The location of the locking set screws make it impossible to remove the humeral head or make positional changes to the humeral head after the humeral stem is engaged in the bone.
With the above shoulder prostheses, once the shoulder prosthesis has been inserted into the patient""s bone, the angular position of the humeral head cannot be changed without removing the humeral stem. Misalignment caused by such factors as incorrect resection are not readily correctable with respect to humeral head alignment.
Consequently, there is a need for a modular shoulder system that can accommodate differences in patient anatomy, particularly with respect to angular positioning of the humeral head with respect to the humeral stem. There is a further need for a shoulder prosthesis that provides version and varus/valgus angulation/positioning that is easily set and reset.
In order to address these needs, the present invention provides a shoulder prosthesis designed to meet the challenges of shoulder replacement surgery. In one embodiment, shoulder prosthesis comprises at least three components, namely a humeral stem, a humeral head, and an adjustment and/or humeral head locking device.
In one form, the subject invention provides a shoulder prosthesis. The shoulder prosthesis includes a humeral stem adapted to be implanted into a humerus and including an expansion receptor, a humeral head defining an articulation surface and a mounting cavity, and an expansion device cooperating with the mounting cavity and the expansion receptor to couple the humeral head to the humeral stem, the expansion device allowing angular positioning of the humeral head relative to the humeral stem and locking of a selected angular position of the humeral head relative to the humeral stem by expansion of the expansion device relative to the expansion receptor.
In another form, the subject invention provides a shoulder prosthesis. The shoulder prosthesis includes a humeral stem having a proximal end and a distal end, the proximal end having a post extending therefrom, the post having tapered threads extending essentially from said proximal end of the humeral stem to an end of said post, a humeral head having an articulation surface and a bottom surface, and a mounting cavity in the bottom surface, and an expansion member configured to be received in the mounting cavity and having a threaded bore adapted to be received on the threaded post, the expansion member allowing humeral head angulation and fixing of a selected humeral head position when the expansion member is advanced onto the threaded bore such that expansion member expands.
In yet another form, the subject invention provides a shoulder prosthesis. The shoulder prosthesis includes a humeral stem having a proximal end and a distal end, the proximal end having an expansion cavity therein, a humeral head having an articulation surface and a bottom surface, and a mounting cavity in the bottom surface, and an expansion device configured to be received in the expansion cavity, the expansion device having an expansion member with a threaded bore and a mounting expander, the mounting expander having a head adapted to receive the mounting cavity of the humeral head and a threaded body adapted to receive the expansion member, the expansion device allowing humeral head angulation and fixing of a selected humeral head position when the mounting expander is advanced onto the threaded bore such that expansion member expands.